The present invention relates to a method of making paper and paper products. More specifically, a laccase, lipase and cationic fixative polymer composition is added to a lignocellulosic suspension to help improve dry strength of the paper and paper products.
Paper pulp is typically processed from wood through the Kraft processes. This process produces a cellulosic fiber with a dark brown color, mostly due to the presence of lignin. For some applications, lignin molecules are further removed by a process known as bleaching to produce bleached fiber suitable for making paper products such as tissue, towel, and printing and writing paper. For other uses such as linerboard, unbleached fiber is preferred because it is economical and also environmental friendly for not going through bleaching process using toxic bleaching chemicals. Unbleached Kraft fiber usually contains 1% to 2% lignin. Although lignin is significantly reduced via the Kraft process, the remaining lignin is embedded in cellulose, resulting in a lignocellulosic material that requires more than 50% of the energy that is needed to refine a bleached fiber mechanically in papermaking processes. Other mechanical pulps such as thermal mechanical pulp (TMP) is another type of unbleached fiber that is widely used for papermaking. Lignocellulosic material is a term used to describe the wood fiber that contains lignin molecules. Many recycled brown furnishes are derived from a mixture of different types of fibers with inferior quality than virgin fibers. Recycled fibers, e.g., old corrugated container (OCC) and waste newspaper, not only contain lignin, hemicellulose and other biomass, but also contain a significant amount of contaminants known as stickies and pitches such as polyvinyl acetate and ester organic contaminants. These types of contaminants can interfere with fiber to fiber bonding resulting in decreased dry strength of the final product.
To restore dry strength properties of the paper product made from recycled lignocellulosic material such as poor quality OCC fiber, papermakers traditionally use synthetic polymeric dry strength additives. The use of enzymes for papermaking has gained popularity steadily due to the rapid developments of robust and inexpensive enzyme products and its environmentally friendly approach. Although cellulases are being used recently for paper dry strength, the commercial success is limited to bleached virgin fiber or deinking pulp (DIP). It is evident that accessibility of cellulase to lignocellulosic fiber is hindered by lignin molecule and other non-cellulosic biomasses bound with the cellulose. Although many commercial trials have been attempted, cellulase is generally not suitable for poor quality recycled lignocellulosic fiber, or short fiber TMP, etc., for dry strength application. Until now, no enzyme technology has achieved significant commercial success in papermaking with recycled OCC fiber, particularly poor quality OCC. Thus, there is a need of an environmentally friendly and sustainable enzyme approach for recycled OCC or unbleached virgin fiber as an alternative technology or a replacement of the synthetic polymeric additives.
Laccases are copper-containing enzymes that are known to be good oxidizing agents in the presence of oxygen and are used for many other applications, including treatment of pulp waste water, pulp de-inking, industrial color removal, bleach for laundry detergents, oral care teeth whiteners. Laccases are being widely investigated for bio-bleaching wood fiber in pulping process as a replacement for toxic chemical bleaching reagents. Laccase is also capable of polymerizing lignin or polyphenols in the wood fiber and thereby widely investigated as a catalyst or a facilitator to improve paper dry strength, either with or without mediators or radical generating chemicals. The likely mechanism for the improved strength was the crosslinking of lignocellulosic fiber through lignin oxidation and polymerization. In addition, laccase may also oxidize other phenolic-containing components such as aromatic side chains in protein, hemicellulose, cellulosic fiber, etc. under specific radical-assisted conditions, to provide functional groups that interact with each other to give paper strength properties. Advantageously, the actions of laccase on lignin and other functional groups generally have no adverse effect on fiber quality such as fiber length under conventional papermaking conditions.
U.S. Pat. No. 6,207,009 disclosed a process for producing paper or paperboard from mechanical pulp in which the pulp is treated with a phenol-oxidizing enzyme, particularly laccase and peroxidase, after mechanical refining of the pulp has been completed. The resulting paper exhibits an increased strength relative to paper produced from untreated pulp. The prior art did not mention any synergistic effect of laccase with lipase and cationic polymers for recycled lignocellulosic fiber. Similarly, U.S. Pat. No. 6,610,172 claimed a process for producing paper materials having improved wet strength. This process involves (a) preparing a suspension of unbleached or semi-bleached chemical or semichemical pulp or pulp from recycled fibers; (b) treating the pulp with a phenol-oxidizing enzyme, e.g., laccase, and a mediator; and (c) de-watering the treated pulp in a papermaking machine to make paper. U.S. Pat. No. 5,603,804 described a process for producing linerboard or corrugated medium using the oxidase-treated pulp. The pulp is unbleached Kraft pulp, neutral sulfite semichemical pulp, or recycled pulp from old corrugated containers or old news print. The oxidases include laccase, or catechol oxidase, or bilirubin oxidase.
US Patent Application No. 2014116635 described a method of making paper or paperboard having enhanced dry strength using a laccase or a cellulase enzyme and a cationic water-soluble polymer. The prior art did not disclose any synergistic effect of laccase with lipase and cationic polymers on OCC recycled fiber.
Lipase or esterase has been commercially used for removing stickies or pitches adhered on the fiber surface in papermaking. Stickies content varies with fiber type and paper mill systems, and it poses a major problem to recycled paper mills, particularly to the Asian or European linerboard mills that routinely use poor quality recycled OCC. Not only do hydrophobic stickies or pitches accumulated on the process machinery to reduce productivity and/or deposit on paper products to lower paper product quality, but also do those hydrophobic organic contaminants interfere with cellulosic fiber-fiber interaction and thereby reducing paper strength. In addition, those hydrophobic contaminants on fiber surface could prevent enzymes and chemical additives from accessing to fiber surface for reaction or interactions, and reduce the efficiency of these reagents.
US Patent Application No. 20070261806 disclosed methods of treating pulp stocks with an enzyme formulation containing one or more oxidative enzymes, to reduce pitch deposition. It described that the pulp stock is treated with an enzyme formulation containing laccases, peroxidases, esterases, and/or combinations thereof. The enzyme formulations may also contain a laccase mediator and/or a dispersant. The enzyme formulation can be applied at any of several locations during the pulping and/or papermaking process, but typically applied as a solution to the pulp stock. The prior art did not discuss the effect of a cationic polymer on laccase and esterase performances, and did not disclose any effect of the formations on paper dry strength property.
Cationic polymers could be used to blend with enzyme to improve enzyme stability and accessibility of the enzyme to cellulosic fiber surface via their fixative property. It could also benefit in fiber retention and COD reduction in recycled paper mills. Those benefits have been proved in the lab and also in many commercial practices.
U.S. Pat. No. 8,454,798 disclosed a method for making paper or paper board by applying a composition containing enzyme and cationic coagulant to papermaking pulp prior to paper forming. However, this prior art did not disclose any synergistic effect of laccase, esterase and cationic polymers on paper dry strength property.
US Patent Application 20140116653 disclosed a method of making paper or paperboard having enhanced dry strength using an enzyme and a polymer including at least one of a cationic water-soluble polymer and an amphoteric water-soluble polymer. The prior did not disclose any information on effect of esterase or lipase on paper strength.
It is known in the art that cationic polymer can be used in combination with enzyme for papermaking uses. Cationic polymers are used together with enzymes for stickies control and strength applications. Those cationic polymers includes poly(diallyldimethylammonium chloride), poly(DMA-Epi) polyamine, polyaminoamide derivatives and polyvinylamine derivatives etc. However, not all the cationic polymers would benefit enzymes performance or stability. As matter of a fact, many cationic polymers reduce or deactivate activity of the enzymes such as laccase and lipase. Polyvinylamine and glycoxylated PAM may covalently react and crosslink enzyme to deactivate the enzyme activity completely. Simply combining an enzyme with a cationic polymer is not a solution to all.
The current method provides a dry strength composition for papermaking to improve dry strength properties of a paper product and also improve the efficiency of the papermaking process. It has been discovered that a combination of laccase and lipase together with cationic polymer with or without a laccase activator provides for synergistic effects in papermaking and produces a paper product with improved dry strength properties. More specifically, the current method relates to the use of a composition to improve dry strength properties of a paper product by treating a pulp furnish containing lignocellulosic unbleached fiber and/or recycled brown stock.
In the current composition, laccase serves as an enzyme to polymerize lignin via oxidization, lipase catalyzes breakdown of organic stickies and pitches on fiber surfaces and improves accessibility of laccase and the fiber to fiber binding interaction. The cationic polymers help in dispersing stickies, stabilizing the laccase and lipase and improves fiber retention. When laccase and lipase were used in combination with a cationic polymer, a synergetic effect was observed. Thus, the invention provides a three-component dry strength composition for use in papermaking application.